In recent years, there has been an increasing demand for portable electronic products such as laptop computers, smartphones, and smartwatches, and the development of devices such as energy storage batteries, robots, and satellites has begun in earnest. Along with this, research into high-performance secondary batteries that can be repeatedly charged and discharged has been more actively conducted.
Examples of currently commercialized secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among such various secondary batteries, lithium secondary batteries are freely rechargeable because of having substantially no memory effect compared with nickel-based secondary batteries, and have a very low self-discharge rate and high energy density. Owing to these merits, there has been high interest in lithium secondary batteries.
In general, lithium secondary batteries use a lithium-based oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material. A lithium secondary battery may include: an electrode assembly in which a positive electrode plate coated with such a positive electrode active material and a negative electrode plate coated with such a negative electrode active material are disposed with a separator therebetween; and an exterior, that is, a battery case, in which the electrode assembly and an electrolytic solution are sealed.
In general, according to exterior types, lithium secondary batteries may be classified into a can type in which an electrode assembly is accommodated in a metal can, and a pouch type in which an electrode assembly is accommodated in a pouch formed of an aluminum laminate sheet.
In recent years, secondary batteries have been widely used not only in small-sized devices such as portable electronic devices, but also in medium to large-sized devices such as automobiles or power storage devices. In particular, along with the depletion of carbon energy and the increasing interest in the environment, there has been worldwide interest in hybrid vehicles and electric vehicles in countries such as the USA, Europe, Japan, and Korea. The core component of such a hybrid or electric vehicle is a battery pack providing driving power to a vehicle motor. Since hybrid or electric vehicles can have driving power via charging and discharging of battery packs, hybrid or electric vehicles have high fuel efficiency and emit no pollutants or less pollutants compared to vehicles only using engines, and thus the use of hybrid or electric vehicles has been gradually and markedly increased.
Most battery modules, particularly, middle to large-sized battery modules for hybrid vehicles, electric vehicles, or energy storage systems (ESSs) include a plurality of secondary batteries, and the plurality of secondary batteries are connected in series and/or parallel with each other for high capacity and power. In addition, pouch-type secondary batteries are generally used in middle to large-sized battery modules because the pouch-type secondary batteries are easy to stack and are light, and a large number of pouch-type secondary batteries can be included in one battery pack.
As the amount of use or application fields of batteries increases along with a large increase in the capacity and output power of batteries, batteries are required to have various characteristics.
A typical one of such characteristics may be cooling performance for effectively cooling battery modules. In particular, the cooling of a battery module in which a plurality of secondary batteries are densely included is a very important task. Secondary batteries may be used in a high-temperature environment such as summer and may generate a large amount of heat by themselves. In this case, if a plurality of secondary batteries are stacked on one another, the temperature of the plurality of secondary batteries may further increase. However, this high temperature may lower the performance of the secondary batteries and even may cause fires or explosions.
In addition, another required characteristic may be the safety of batteries. In particular, battery modules may catch on fire because of various causes such as overcharging, overdischarging, or penetration by acicular parts. In this case, if the fire is not extinguished in the early stage, the battery modules may explode, or the fire may spread to other devices such as automobiles. This may cause severe loss of property and lives.
In addition, another characteristic necessary for batteries may be improved energy density. A secondary battery is a part of a battery module contributing to an increase in energy, and thus if parts other than the secondary battery occupy a large space in the battery module, the output power or capacity of the battery module may decrease even though the volume of the battery module increases. Therefore, in this case, the battery module may have low energy density, and thus it may be difficult to decrease the size of the battery module or improve the capacity or output power of the battery module.